I've used an F1 for years, since it is usually bouncing around in the back of my vehicle somewhere. I have more expensive ones, but the F1 does a LOT of work for me and takes the abuse. It isn't as finicky about shotgun loads either. I have a couple that simply refuse to give consistent readings for shot shells. They work fine with rifles and handguns.

I have a chrony, but I didn't completely trust it so I bought an Oheler proof channel. (two readings for each shot) Just to see how far off the Chrony was, I set it up behind the Oheler. After correcting for the extra distance there was no stastically significant difference in the three readings. The Oheler is easier to use as it has a built-in printer, but probably not worth the cost. Bud Wood

Be sure to use the diffusers, especially in direct sunlight. You can also experiment with distances. Some chronographs I've had to move back and some work better a little closer. I also put a small piece of plexiglass in front of the f1. It keeps the display from getting too much debris stuck to it.

I never could figure out how to use the diffusers without the sun directly overhead. If you tilt the unit to have the shadow cover the openings (when the sun is at an angle) you change the distance between them,a nd therefore the readings.

It seemed like my readings have been 50-75FPS faster than what the books say they should be. To check I took new STS 2.75 gram,# 8 which is suppose to be 1145FPS and they were 50-60 FPS faster than they should be and I took new NITRO # 7 1/2 shells that say they should be 1235 FPS and they were 1276-1314 FPS. Is this common or is it because of the warmer temps 75-80 degrees and they are made for all weather shooting which would probably lower the speed. Anyone else have this same problem? It seems consistantly 50-75 FPS fast with all reloads or factory shells. Kind of fun to monkey with. Glenn

Glenn, it's partly the choke I think. My guess is that you are using a full; if you used cylinder you would knock off maybe 30 ft/sec. How close to the chronograph are you? I use about 6 feet and set things up as illustrated in the link above.

When I don't use my diffuser/cover I try to pick a cloudy day as has been suggested above.

The choke can have a marked effect on the velocities. I use the most open choke I have on hand, which is usually true cylinder or a very open skeet choke. Going from one of those to a "real" full choke can show an increase of 50 fps or more as measured with some loads. It may not always be that a big difference, but a difference none the less. I suspect that even my cylinder bore chokes will show a higher reading over a light triggered set of screens than the same load would through the induction screens. Loads I have had tested elsewhere have usually shown lower velocities than my chronograph.

Maybe this is a dumb question but are you using the choke you will be shooting for "real"? If I wanted to know the velocity of my trap load I'd sure be using the full or IM choke tube. (I do, but just want to know if I understand why you would use an open choke, unless you are shooting skeet and want to know the velocity of the skeet load)

Unless you spring for a very costly chronograph made for shotshell use, your unit is intended for clocking bullets and starts and stops when the first object crosses the photocells. With shotshells, they clock the leading pellet where chronos made for shotshells clock the mass of the payload. Tighter chokes lengthen that mass, making the readings artificially higher. My chronograph manufacturer told me that deducting 35 fps from my unit's readings should get me very close to the actual speed.

Those +/-$100 chronographs are very good for their cost. Last year, I bought a much more expensive Pact, thinking I was getting something better. It wouldn't do anything but register "FIRE" and their tech support, which the instructions strongly encourage you to call in the event of a problem, kept telling me that I had to tilt the unit so the sunshades were casting a shadow over the photocells. When I told them that the sun was behind me and that doing that would require my shooting ACROSS the range, they said I should do that! I set up my old cheap chrono, which worked fine with the sun behind it, and returned the Pact.